Field of the Invention
This invention relates to cyanoacrylate compositions that include, in addition to the cyanoacrylate component, a rubber toughening component, which is substantially clear and colorless and which is substantially free of release agents and anti-oxidants known to impair the fixture speeds and shelf life stability of cyanoacrylate compositions to which they are added. As a result, the inventive rubber toughened cyanoacrylate compositions demonstrate improved properties, such as fixture speed, strength and shelf life under accelerated aging conditions.
Brief Description of Related Technology
Cyanoacrylate adhesive compositions are well known, and widely used as quick setting, instant adhesives with a wide variety of uses. See H. V. Coover, D. W. Dreifus and J. T. O'Connor, “Cyanoacrylate Adhesives” in Handbook of Adhesives, 27, 463-77, I. Skeist, ed., Van Nostrand Reinhold, New York, 3rd ed. (1990). See also G. H. Millet, “Cyanoacrylate Adhesives” in Structural Adhesives: Chemistry and Technology, S. R. Hartshorn, ed., Plenun Press, New York, p. 249-307 (1986).
U.S. Pat. No. 4,440,910 (O'Connor) pioneered rubber toughened cyanoacrylate compositions through the use of certain organic polymers as toughening additives that are elastomeric, i.e., rubbery, in nature. The '910 patent is thus directed to and claims a curable adhesive comprising a substantially solvent-free mixture of: (a) a cyanoacrylate ester, and (b) about 0.5% to about 20% by weight of an elastomeric polymer. The elastomeric polymer is selected from elastomeric copolymers of a lower alkene monomer and (i) acrylic acid esters, (ii) methacrylic acid esters or (iii) vinyl acetate. More specifically, the '910 patent notes that as toughening additives for cyanoacrylates, acrylic rubbers; polyester urethanes; ethylene-vinyl acetates; fluorinated rubbers; isoprene-acrylonitrile polymers; chlorosulfinated polyethylenes; and homopolymers of polyvinyl acetate were found to be particularly useful.
The elastomeric polymers are described in the '910 patent as either homopolymers of alkyl esters of acrylic acid; copolymers of another polymerizable monomer, such as lower alkenes, with an alkyl or alkoxy ester of acrylic acid; and copolymers of alkyl or alkoxy esters of acrylic acid. Other unsaturated monomers which may be copolymerized with the alkyl and alkoxy esters of acrylic include dienes, reactive halogen-containing unsaturated compounds and other acrylic monomers such as acrylamides.
One group of elastomeric polymers are copolymers of methyl acrylate and ethylene, manufactured by DuPont, under the name of VAMAC, such as VAMAC N123 and VAMAC B-124. VAMAC N123 and VAMAC B-124 are reported by DuPont to be a master batch of ethylene/acrylic elastomer.
Henkel Corporation (as the successor to Loctite Corporation) has sold for a number of years since the filing of the '910 patent rubber toughened cyanoacrylate adhesive products under the tradename BLACK MAX, which employ as the rubber toughening component the DuPont materials called VAMAC B-124 and N123. In addition, Henkel has sold in the past clear and substantially colorless rubber toughened cyanoacrylate adhesive products, namely, LOCTITE 4203, 4204 and 4205, which employ as the rubber toughening component the DuPont material, VAMAC G. While VAMAC G contains no fillers to provide color or stabilizers, it does contain processing aids. These processing aids—or release systems—are reported to be ARMEEN 18D and stearic acid in combination with GAFAC RL-210 (or with VANFRE UN, ZELEC UN or SERVOXYL VPAZ-100). In addition, it is believed that polyethylene glycol ether wax is also used as a processing aid. Waxes such as this interfere with the physical properties of cyanoacrylate compositions.
VAMAC VCS rubber appears to be the base rubber, from which the remaining members of the VAMAC product line are compounded. VAMAC VCS is a reaction product of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, which once formed is then substantially free of processing aids such as the release agents octadecyl amine, complex organic phosphate esters and/or stearic acid, and anti-oxidants, such as substituted diphenyl amine.
Recently, DuPont has provided to the market under the trade designation VAMAC VMX 1012 and VCD 6200, which are rubbers made from ethylene and methyl acrylate. It is believed that the VAMAC VMX 1012 rubber possesses little to no carboxylic acid in the polymer backbone. Like the VAMAC VCS rubber, the VAMAC VMX 1012 and VCD 6200 rubbers are substantially free of processing aids such as the release agents octadecyl amine, complex organic phosphate esters and/or stearic acid, and anti-oxidants, such as substituted diphenyl amine, noted above.
Thus, notwithstanding the state-of-the-technology and the commercial success experienced by Henkel Corporation with its line of rubber toughened cyanoacrylate adhesive products (such as LOCTITE BLACK MAX 380 and 480 and LOCTITE 4203, 4204 and 4205), it would be desirable to provide a substantially clear and colorless rubber toughened cyanoacrylate composition, which demonstrates improved fixturing speed and shelf life stability compared to known rubber toughened cyanoacrylates.